1. Field of the Invention
The present invention relates to a UHV (Ultra High Voltage) breaker used in an ultra high voltage power plant such as the substation on a million-volt power supply system line and, more particulaly, a resistance-provided breaker wherein resistance contacts for allowing making and breaking to be achieved through resistances are connected parallel to main contacts for allowing making and breaking to be achieved through no resistance.
2. Description of the Related Art
The breakers provided with making resistances have been well-known as being suitable for 500,000 volts power supply system. When power is added to the unloaded transmission lane, large overvoltage results. In order to suppress this overvoltage, the breaker of this kind is arranged to make resistances operative about 10 ms before the main contacts are connected. After the overvoltage is thus suppressed in this manner, the main contacts are connected.
One of these making-resistance-provided breakers is shown in FIG. 1. In the case of the resistance-provided breaker shown an FIG. 1, a cylindrical breaker tank 6 has a manhole 7. Main contacts 1 connected to external conductors 5 are housed in the cylindrical breaker tank 6. Main contacts and resistance contacts 2 are arranged parallel to the longitudinal center axis of the tank 6. The main contacts 1 and resistance contacts 2 are arranged to align their end positions with each other. A resistance 3 connected in series to each resistance contact 2 is arranged in a space between the main contacts 1 and the resistance contacts 2 in the longitudinal direction of the tank 6. The main contacts and resistance contacts 2 are connected to the operation mechanism 4 through crank mechanisms 8.
According to the conventional engineering having the above-described arrangement, each resistance 3 can be conveniently housed in the space between the main contacts 1 and the resistance contacts 2. This enables the breaker to be made smaller in size.
Power supplied through the transmission line becomes higher and higher in voltage and power of ultra high voltage such as one million volts is planned to be supplied through the transmission line. In the case of the UHV breaker used for this transmission line, resistances are inserted parallel to the main contacts at the time of breaking. The rise of recovery voltage caused in the main contacts after the breaking of the breaker is thus reduced to make the breaking easy. Resistances are also inserted parallel to the main contacts to suppress overvoltage caused after the breaking when earthed. It is needed that these resistances are separated from the circuit 30-40 ms after the breaking of the main contacts is finished. This makes it necessary that the resistances are connected parallel to the main contacts and that resistance contacts are also arranged in series to the resistances to select the timing at which the resistances are separated from the circuit.
It is therefore supposed that the making resistances and the making resistance contacts used for the 500,000 volts breaker are commonly used as those resistances and contacts which are needed for the UHV breaker at the time of breaking or after the breaking.
In the case of the UHV breaker, however, each resistance is needed to have a heat capacity 30 or 40 times larger than that of the resistance used for the 500,000 volts breaker, because voltage becomes doubled and the time during which power is supplied becomes 3 or 4 times. In short, each resistance for the UHV breaker must be made larger in size to have such a large heat capacity. When the conventional resistance-provided breaker shown in FIG. 1 is to be used as the UHV breaker which needs larger-sized resistances. However, the volume of each of the resistances 3 becomes so large as to create a large unnecessary space in the tank 6, as shown in FIG. 2. The resistance contacts 2 serve only to achieve making operation in the case of the 500,000 volts breaker, but it is needed in the case of the UHV breaker that resistance current is shut off after the breaking of the main contacts 1 is finished. Further, the resistance contacts 2 are asked to achieve a complicated operation in such a way that they are opened 30-40 ms after the main contacts 1 when power is shut off. The linkage system including the operation and crank mechanisms 4 and 11 must be therefore made more complicated and larger in size.
On the other hand, the breaker must be designed in such a way that its insulation recovering characteristics becomes quicker as voltage used becomes higher and higher. The breaker section of the UHV breaker, as described above, must have the high speed opening system. It is therefore preferable that the linkage system for connecting the operation mechanism 4 to the breaking section is made as simple as possible in structure to enable the breaker to have high reliability. In other words, it is quite important in order to enhance the reliability of the breaker how compactly the main contacts 1, the resistance contacts 2 and the resistances 3 can be housed in the tank 6 and how simple the linkage system for connecting the operation mechanism 4 to the breaking section can be made in structure.
In the case of the UHV breaker as described above, however, all of the components become large in size and particularly the resistances 3 becomes the largest of all. It is therefore impossible to make the breaker compact unless the conventional arrangement of the resistances 3 in the tank 6 is changed.
In the breaker of this kind, each main contacts 1 is usually supported in cantilever manner by a box-like center piece member (not shown) which is arranged in the center of the tank 6 and which has high mechanical strength. In the case of each resistance contacts 2 which is arranged parallel to the main contacts 1, therefore, its end portion which is located on the center side of the tank is also supported in cantilever manner by the center piece. When the resistances 3 is small in size and light in weight as seen in the case of the 500,000 volts breaker shown in FIG. 1, it can be supported by the front end of the resistance contacts 2 which is supported in cantilever manner by the center piece. In the case of the UHV breaker shown in FIG. 2, however, each resistances 3 is large in size and heavy in weight. It becomes difficult, therefore, to support the resistances 3 only by the front end of the cantilever-supported resistance contacts 2. It is necessary for the conventional UHV breaker to have a support insulator 10 arranged between the resistance contacts 2 and the resistances. The mechanism described above is very complicated. Unless these support insulators are added to the breaker, there is fear that some components become loose and come out of the breaker when the breaker is being transported or when it is used.